1. Field of the Invention
This invention relates to an optical information recording/reproduction apparatus, and more particularly relates to an optical information recording/reproduction apparatus which is capable of eliminating offset due to generation of stray light (light emitted from a light emitting element which is incident directly to a light receiving element not by way of a recording medium) in a focus error signal and/or tracking error signal.
2. Description of Related Art
A pickup module having a light emitting element (for example, a laser diode) and a light receiving element (for example, photo diode) in a unit has been developed in order to realize a small sized, thin, and highly reliable optical pickup used for CD (Compact Disk) or MD (Mini Disk), or the like.
In the above-mentioned pickup module, stray light that is a light emitted from a light emitting element incident directly to a light receiving element not by way of a recording medium can be generated. As the result, in the case that the intensity of a stray light is relatively larger than that of returning light (the light that is reflected by the optical disk surface and returned on the same optical path out of the light emitted from the light emitting element), the stray light causes the offset which is not negligible in a focus error signal and/or tracking error signal.
For example, in the case of an optical disk for only reproduction such as CD, the relation between the focus error signal and the offset due to the stray light is shown in FIG. 12A. As shown in FIG. 12A, a focus error signal is a signal of S-shaped characteristic. In the case of CD, because the reflectance of the light is as high as about 70%, the proportion of the offset due to the stray light is relatively smaller than that of the focus error signal.
On the other hand, in the case of the writable optical disk such as CD-RW (Compact Disk-ReWritable) and DVD-RAM (Digital Versatile Disk-Random Access Memory), the relation between the offset due to the stray light and the focus error signal is shown in FIG. 12B. FIG. 12C is a diagram which is obtained by amplifying the focus error signal shown in FIG. 12B so that the amplitude is equal to that of S-shaped curve shown in FIG. 12A. As shown in FIG. 12B and FIG. 12C, in the case of the writable optical disk such as MD, CD-RW, and DVD-RAM, because the light reflectance is as relatively as low as 10 to 30% (returning light is reduced) in comparison with in the case of CD-ROM, the proportion of offset due to the stray light is relatively larger than that of the focus error signal and is not negligible.
FIG. 13A shows a diagram obtained by offsetting the offset due to the stray light with adding electric offset to the focus error signal shown in FIG. 12C.
However, this method is disadvantageous in that the offset component due to stray light re-appears as shown in FIG. 13B when the sensitivity of a light receiving element is changed concomitantly with the external temperature change or when the emission power of a light emitting element becomes large from the state of FIG. 13A.
Furthermore, as shown in FIG. 13C, even in the case that the gain is applied to the focus error signal shown in FIG. 13B so that the amplitude is equalized to the amplitude of the S-shaped curve shown in FIG. 13A, this method is disadvantageous in that the offset is generated.
The present invention was accomplished to solve the above-mentioned invention, it is the object of the present invention to provide an optical information recording/reproduction apparatus which is capable of eliminating the offset in the focus error signal to 0 even when the sensitivity of a light receiving element is changed due to external temperature change or when the emission power of a light emitting element becomes large.
An optical information recording/reproduction apparatus of the present invention comprises a light emitting means for emitting a beam to an optical recording medium, a light receiving means for receiving a returning light from the recording medium disposed near the light emitting means, a focus error operation means for computing a focus error signal using an electric signal generated from the light receiving means, and a tracking error operation means for computing a tracking error signal using an electric signal generated from the light receiving means, wherein the configuration of the light receiving means is optimized so that the offset of an electric signal sent out to at least one of the focus error operation means and the tracking error operation means is equalized to approximately 0.
In the information recording/reproduction apparatus of the present invention, the configuration of the light receiving means is optimized so that the offset is equalized to approximately 0.